This invention relates to an internal combustion engine and a method.
It is known that internal combustion engines, in particular gas engines, can be designed as direct ignitors with a displacement volume of up to approximately 3 liters. In the case of direct ignitors, a spark plug protruding into the main combustion chamber directly ignites the gas/air mixture present in the main combustion chamber. The disadvantage of direct ignitors is that the quality of the ignition of the gas-air mixture depends entirely on the spark plug. Even minimal wear and tear of the spark plug becomes noticeable due to cycle fluctuations (fluctuations in the center of gravity of the combustion). However, to operate at maximum efficiency, it is important to operate the internal combustion engine as close as possible to the knocking limit. Despite this, if cycle fluctuations must be considered, the internal combustion engine must be operated further away from the knocking limit and thus at reduced efficiency. In such internal combustion engines, which have no prechambers, it is customary, by using specially designed spark plugs, pistons (e.g. recessed pistons) and a special cylinder head, and by closing the intake valve after the piston has left its bottom dead center (late Miller or Atkinson cycle), to achieve swirling of the charge in the main combustion chamber and thus a more homogeneous combustion.
It is also known that by flushing the prechambers with pure gas or a very rich gas-air mixture (lambda approximately equal to 1.1) in the case of internal combustion engines equipped with prechambers (generally with a displacement volume of approximately 3 liters), the mixture in the prechamber can be made to be readily flammable. At the time of ignition, a lambda of around 1.0 to 1.1 occurs in the prechamber. This is referred to as gas-flushed prechambers. The ratio of the volume of the prechamber to the volume of the main combustion chamber in the top dead center (compression volume) is frequently around 1% for such prechamber engines.
Gas-flushed prechambers generally have a fuel-gas supply which is separate from the supply of the main combustion chambers. This fuel-gas supply generally comprises a prechamber gas compressor which serves to bring the fuel gas intended for the prechamber to the level of the charge-air pressure or higher to generate a positive pressure gradient across the prechamber gas valve (generally a non-return valve). The costs for the prechamber gas compressor and the prechamber gas control path are considerable, meaning that this technology is not used for smaller gas engines (with a stroke volume of up to approx. 3 liters).
It is also known that an intake valve can be closed before a piston has reached its bottom dead center in the intake stroke (early Miller cycle).